An ink jet image forming apparatus, for example an ink jet printer, is in widespread use, because of low running costs and ease in forming a colored print image and in reducing the size of the apparatus. This ink jet printer is configured for emitting a minor quantity of the ink from small-sized ink emitting openings formed in an ink emitting surface of a print head to record an image. If the printing operation has not been performed for an extended period of time, such that the ink has not been emitted from the ink emitting openings in the print head for prolonged time, the ink deposited to near the ink emitting openings formed in the ink emitting surface by the last printing operation tends to be vaporized or dried, that is, thickened or solidified, with the result that it is difficult to effect normal ink emission.
In such ink jet printer, it has been known that, if the ink is emitted from a given ink jet opening in order to effect printing on a recording medium, and subsequently the ink is not emitted on end for several to tens of seconds, the ink deposited to or near the ink emitting opening formed in the ink emitting surface tends to be vaporized or dried, that is, thickened or solidified. For this reason, the ink is preliminarily emitted even during the time interval the printing operation is not performed, in order that the ink deposited to or near the ink emitting opening formed in the ink emitting surface by the previous printing operation is not vaporized and dried, that is, thickened and solidified.
On the other hand, in the preliminary ink emission from the ink emission opening, the preliminary emission is carried out in a constant quantity, without dependency on the size of the recording medium.
With the conventional technique, described above, the quantity or the color of the ink preliminarily emitted from the ink emitting opening is not controlled in the operation of the preliminary ink emission in the ink jet printer, in dependence upon the quantity of the ink emitted last time from the ink emitting opening, image data or the color of the emitted ink, with the consequence that the quantity of the ink used in the preliminary ink emission is increased.
With the conventional technique, described above, control of the quantity of the preliminary ink emission from given ink emitting openings or selection of the ink emitting openings in the operation of the preliminary emission of the ink jet printer is not made in dependency upon the ink emitting position during the printing operation prior to the operation of the preliminary emission via the ink emitting openings, with the consequence that the quantity of the ink used in the preliminary ink emission is increased. Moreover, in the conventional operation of the preliminary ink emission, the operation of the preliminary ink emission is made at a constant quantity at every ink emitting opening regardless of the size of the recording medium, so that the ink is preliminarily emitted from ink emitting openings for a non-printed space on the recording medium, if there is such space, thus leading to wasteful consumption of the preliminarily emitted ink.
In order to prevent the large consumption of ink due to the preliminary ink emission, it may be contemplated to use a blade to clean the ink emitting openings. However, a certain quantity of the ink tends to be left in the vicinity of the ink emitting openings by such wiping with the blade, with the result that sufficient cleaning cannot be achieved.
Meanwhile, if plural blades are mounted on a rotary shaft for rotation, there is still the risk of damaging the ink emitting surface. In addition, since reliance is placed only on the wiping effect, there is presented a problem that the ink is left in the vicinity of the ink emitting openings.